Device for cracking organic products in liquid phase by means of an electric arc

ABSTRACT

A device for the cracking of organic products in liquid phase by means of a submerged intermittent electric arc wherein the electric arc is produced between stationary electrodes and movable electrodes which are secured to a rotary support at uniform angular intervals over a circumference which is cocentric with the axis of rotation of said support. The stationary electrodes and the movable electrodes which are in cooperating relation therewith are so arranged that the free extremities of the movable electrodes come successively into contact with the free extremities of the stationary electrodes in a plane at right angles to the axis of rotation of the movable electrode support.

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States DEVICE FOR CRACKING ORGANIC PRODUCTS 7 IN LIQUID PHASE BY MEANS OF AN ELECTRIC ARC 8 Claims, 3 Drawing Figs.

US. Cl 204/326, 204/l7 l 204/172 llnt. Cl C22d 7/08 Field of Search 204/325,

References Cited Primary Examinerl-loward S. Williams Assistant Examiner--Neil A. Kaplan Altorney-woodhams, Blanchard and Flynn ABSTRACT: A device for the cracking of organic products in liquid phase by means of a submerged intermittent electric arc wherein the electric arc is produced between stationary electrodes and movable electrodes which are secured to a rotary support at uniform angular intervals over a circumference which is cocentric with the axis of rotation of said support. The stationary electrodes and the movable electrodes which are in cooperating relation therewith are so arranged that the free extremities of the movable electrodes come successively into contact with the free extremities of the stationary electrodes in a plane at right angles to the axis of rotation of the movable electrode support.

DEVICE FOR CRACKING ORGANIC PRODUCTS 1N LIQUID PHASE BY MEANS OF AN ELECTRIC ARC The present invention is directed to an improved device for cracking organic products in liquid phase and in the pure or mixed state by means of a submerged intermittent electric arc in order to produce a gaseous mixture (examples of such organic products being the hydrocarbons and their substituted derivatives such as the alcohols, phenols, amines and the like). It is apparent that the constituents of the gaseous mixture obtained depend on the nature of the starting products and that the composition of a starting mixture can also be adapted to influence the composition of the gaseous mixture to be obtained.

There has already been proposed for the production of gaseous mixtures a process which consists in principle in producing between two electrodes submerged in a liquid hydrocarbon an electric arc which is suppressed then restored at a predetermined frequency while imparting to at least one of the electrodes a reciprocating movement which brings the electrodes into contact in order to strike the arc and separates said electrodes in order to extinguish the arc. French Pat. No. 1,296,664 of May 9, 1961 describes a process of this type whereby a gaseous composition which is rich in acetylene and in ethylene can be obtained in conjunction with an excellent energy yield. Said process is essentially distinguished by the fact that the electrodes are mounted in such a manner that a shock which has the effect of cleaning the undesirable carbon deposits inevitably formed at the tips of carbon electrodes should take place at the moment when the contact which results in production of the arc is established.

A first type of reactor which has been constructed for the practical application of this process comprises a set of axially adjustable stationary electrodes, said electrodes being insulated from the ground and connected through an inductance coil to a transformer which delivers a voltage of the order of 500 v. in single-phase current at 50 c./s. and a moving system which is adapted to carry a corresponding number of electrodes subjected to a rectilinear back-and-forth movement which establishes periodically between the stationary and movable electrodes the contact which is necessary both for striking the arc and for cleaning said electrodes.

The back-and-forth movement referred to was obtained by means of a crank rod driven by a synchronous motor having a speed of rotation of 3,000 rpm. By virtue of suitable timing of the movement relative to the phase of the arc current, it was possible to produce a short circuit between the electrodes at a precisely defined moment, namely at the beginning of the halfwave, when the instantaneous voltage attains, for example, a value of 100 volts. This condition was necessary in order to ensure reliable arc formation. The are was extinguished automatically under the combined action of the separation of the electrodes and the transition of the voltage from zero value to the end of the half wave (with reversal of polarity).

However, the industrial application of a device in accordance with this design concept resulted in the construction of a moving system of relatively substantial weight which had to be displaced within the liquid hydrocarbon at a rate of 3,000 times per minute with a range of travel of the order of 60 mm. (this amplitude being found necessary in the case of a voltage of 500 v. applied to arcs in series) and it has proved difficult in practice to develop durable mechanical means for the execution of this movement. In addition, this device makes it necessary to utilize two reactors in order to make full use of a single-phase current supply, the movements of the moving systems of both reactors being displaced by 180 relative to each other.

In order to circumvent these difficulties, it was proposed in the first certificate No. 84,649 filed on Nov. 4, 1963 as an Addition to the above-cited French Pat. No. 1,296,664 to substitute for the rectilinear backand-forth movement of the movable electrodes a reciprocating curvilinear movement and especially a pendular movement. This arrangement has permitted the construction of an apparatus in which the two half waves of the single-phase current could readily be utilized by virtue of a symmetrical assembly of stationary electrodes located on each side of a moving system which was adapted to carry electrodes disposed symmetrically in pairs. The type of reactor just mentioned operated at a voltage of 500 v., a current intensity of 1,000 amps. and a curvilinear range of travel which could be adjusted up to mm. However, the mechanical difficulties entailed in the execution of this movement have not made it possible to ensure satisfactory operation over an appreciable length of time at a speed of 3,000 r.p.m.

In accordance with the present invention, a novel concept has been devised in order to remove the mechanical difficulties which have just been set forth while retaining excellent result in regard to gas yield. This result is achieved by utilizing under predetermined conditions a rotary movement of movable electrodes which are intended to cooperate with stationary electrodes.

It is an acknowledged practice to make use of systems in which movable electrodes are endowed with a movement of rotation with respect to stationary electrodes, especially for the cracking of liquid hydrocarbons. However, by reason of a number of common design characteristics, these systems carry major disadvantages which have excluded the possibility of actual use on an industrial scale.

In point of fact, in all systems of this type which are at present known, the longitudinal axis of the movable electrodes is located at right angles to the axis of rotation of the moving system on which they are supported; said electrodes are usually secured radially at the periphery of a disc to which is imparted a movement of rotation about an axis which passes through the center thereof and are intended to cooperate with stationary electrodes which are disposed at uniform angular intervals around said disc. The majority of propositions which have been directed in the past to this particular design have also indicated the need to ensure that there is no contact between the movable electrodes and the stationary electrodes. This is a primary cause of faulty operation of the electrodes. 1n has in fact been learned by experience that the absence of contact between electrodes in a medium which is as dielectric as liquid hydrocarbons in particular has the first consequence of entailing a very high ignition voltage in respect of a low arcing voltage; furthermore, the carbon deposits which inevitably occur at the tips of carbon electrodes tend to accumulate unless cleaning is resorted to and thus rapidly make the apparatus unserviceable.

On the other hand, if it is sought in devices of the type mentioned above to provide a contact between the movable electrodes and the stationary electrodes, this contact can only be a point contact inasmuch as the end face of each movable electrode is displaced along a curved surface and not a flat surface. In point of fact, a point contact of this kind is unreliable and cannot ensure the stability of arc ignition which is essential in order to ensure satisfactory operation of the reactor. Moreover, by reason of the fact that the movement of rotation of the movable electrodes takes place about an axis which is perpendicular to the longitudinal axes of these latter, the wear of electrodes which occurs during operation causes a reduction in the travel of the movable electrodes and consequently in the length of arc. This phenomenon entails the need for either a starting voltage which is too low and results in poor efficiency or a progressive reduction in voltage during operation, the terminal voltage of an arc being known to be substantially proportional to the length of the are within the range of high current intensities which are employed in industrial service; this reduction in voltage produces a progressive decrease in power which is detrimental to industrial operation in which it is desired to ensure a constant rate of production.

The device in accordance with the invention wherein, as is generally known, the movable electrodes are secured to a rotary support at uniform angular intervals over a circumference which is concentric wit the axis of rotation of said support, is essentially characterized in that the stationary electrodes and the movable electrodes which are in cooperating relation therewith are so arranged that the free extremities of the movable electrodes come successively into contact with the free extremities of the stationary electrodes in a plane at right angles to the axis of rotation of the movable electrode support, means being provided in a manner known per se for adjusting the position of the stationary electrodes with respect to the movable electrodes.

In the construction according to the invention, provision can be made for any number of pairs of movable electrodes in cooperating relation with two stationary electrodes. The diameter of the circumference over which said electrodes are distributed is determined according to the available voltage so that the linear displacement thereof during 1 half-cycle of the current should correspond to the length of are which results from said voltage. For example, in the case of a voltage of 500 v. in single-phase current, the flat contacts of the movable electrode must describe a portion of circumference approximately 150 mm. in length, which corresponds to a diameter of rotation (or to a spacing of the stationary electrodes) of approximately 100 mm. In the case of an apparatus which is supplied with single-phase current at a frequency n and which comprises 2 p movable electrodes, the speed of rotation N in rpm. is given by the formula:

It should be pointed out that it is possible to juxtapose or combine a number of devices according to the invention in order to work in polyphase current. For example, in the case of Two-phase current, provision can be made for two opposite pairs of stationary electrodes and between these two pairs for a rotary moving system having a double face, there being mounted on each face one set of movable electrodes associated with one of said pairs of stationary electrodes.

Apart from the fact that the device in accordance with the invention has all the advantages of known rotary systems in regard to useful travel for the arcs which are produced and in regard to the rational utilization of alternating current halfwaves, it should be pointed out that the arrangement of the plane of contact of electrodes at right angles to the axis of rotation of the moving system has the advantage of ensuring constancy of the path over which each arc travels, this being the case irrespective of the degree of wear of the electrodes. There corresponds to this constant travel a voltage which is also constant, thereby resulting in optimum efficiency and a better possibility of industrial utilization.

Furthermore, the device in accordance with the invention makes it possible to obtain an excellent contact between electrodes which is comparable in every respect with the contact obtained by means of a back-and-forth movement of electrodes. In both cases, this contact takes place between the flat surfaces of the respective extremities of the movable and stationary electrodes as a result of pressure in the case of the back-and-forth movement and as a result of friction in the case of the rotational movement which is carried out in accordance with the invention. The result thereby achieved is a very substantial stability in the ignition of arcs which is essential in order to ensure satisfactory operation of the reactor.

Moreover, the frictional force which is exerted between the flat surfaces of the extremities of the stationary and movable electrodes effects a constant cleaning of the carbon deposited on said extremities during operation. The means provided for adjusting the positions of the stationary electrodes make it possible to restore the best conditions of contact and of friction when the wear of said electrodes makes such an adjustment necessary.

In the practical application of the invention, it has been proved advantageous to adopt a number of special arrangements in the structural design of the movable-electrode support and in the assembly of said electrodes on said support. In

rotation of a moving system of this type in the liquid product to be processed inevitably produced a very low pressure zone behind each electrode by reason of the rate of displacement of the electrodes which can easily attain 15 meters per second; the are which was initiated at the tip of said electrode was then drawn behind this latter and destroyed the retaining metal sleeve in a very short time, thereby rapidly leading to failure of the electrode after this latter had been subjected to repeated impacts under shear stress.

According to a preferred embodiment of the invention, the disadvantages noted in the foregoing have been removed by forming the rotary support which carries the movable electrodes by means of radial arms distributed in a number corresponding to the number of movable electrodes about a common hub, the front portions of the movable electrodes (considered in the direction of rotation) being inserted in the faces of said radial arms which are located opposite to the stationary electrodes whilst the projecting rear portions of said movable electrodes are left free. This arrangement does not entail the suppression of the rear low-pressure zone but only eliminates the destructive action of the arc inasmuch as this latter becomes attached to a carbon surface which affords effective resistance thereto instead of becoming attached to the support sleeve which would otherwise have been destroyed by the are as a result of surface breakaway. In point of fact, the mode of attachment which characterizes this embodiment frees a portion of the electrode surface in order that the arc can adhere thereto without any attendant disadvantage.

As a preferable feature, the arms which carry the movable electrodes are designed in the form of fins each having a portion of surface which is inclined in the direction of rotation in order to facilitate their penetration at high velocity into the liquid product to be processed. The movable electrodes are advantageously designed in the form of prisms having a trapezoidal cross-sectional shape, one of the bases of which constitutes the flat contact face of the electrode. Said electrodes can be locked in position by keying after insertion in the rotary support.

By reason of the stresses carried by the electrodes which are in principle made of a material containing carbon, said electrodes should preferably be endowed with sufficiently high strength. The primary mechanical parameter which provides a criterion of this property is bending strength. There can accordingly be employed for this purpose high-density graphites which have high mechanical strength and especially a bending strength which is greater than 300 kgs./cm

One form of construction of the system in accordance with the invention is shown by way of nonlimitative example in the accompanying drawings, in which:

FIG. 1 is a diagrammatic vertical cross-sectional view of an equipment unit comprising two movable electrodes which are adapted to cooperate with two stationary electrodes;

FIG. 2 is a front view on a larger scale showing the moving system;

Fig. 3 is a profile view of the moving system in the direction of the arrow F of FIG. 2.

As shown in FIG. 1, the apparatus comprises a reaction vessel l which is filled with the liquid product to be processed. Two stationary electrodes which are designated by the reference numerals 2 and 2' are attached to the extremities of two supports 3, 3 which are disposed horizontally one above the other and which are adapted to penetrate into the vessel 1 through suitable leak-tight packings 4, 4 which are fitted in one of the lateral walls of said vessel; the position of said electrodes 2, 2' can be adjusted longitudinally, for example by means of a rack and pinion mechanism 5-6 and 5'-6. Said electrodes are connected to the electric supply system by means of a transformer 7 with interposition of an inductance coil 8 having a suitable impedance.

A unit comprising two movable electrodes 9, 9' is disposed opposite to the stationary electrodes 2, 2' within the interior of the reactor vessel 1 and are fixed on a support which is generally designated by the reference numeral 10. Said support is rigidly fixed to a horizontal shaft 11 which penetrates into the vessel through a leak-tight packing 12 formed in the vessel wall on the side opposite to the packing which carries the stationary electrodes 2, 2'. A movement of rotation in the direction indicated in the figure by the arrow f can be imparted to said horizontal shaft under the action of an electric motor (not shown in the drawings).

in the example which is shown in detail in FIGS. 2 and 3, the support has two arms 13, 13 which are integral with a common hub 14 and extend on each side of this latter both radially and symmetrically with respect to the axis of the shaft 11. The hub 14 is keyed on the shaft 11 by means of a key 15 at a predetermined keying angle a in order to produce a short circuit between movable electrodes and stationary electrodes at the moment when the instantaneous voltage attains a suitable value to ensure reliable arc ignition. In this example, the

arms 13, 13' have the shape of fins, the contour of each fin having substantially the shape of a circular sector and that face of each fin which is directed towards the stationary electrodes 2, 2 has a flat portion 13a and a portion 13b which is inclined in the direction of rotation as indicated in the figure by the arrow f. The movable electrodes 9, 9' are designed in the form of prisms each having a contact base of trapezoidal shape and are inserted in diametrically opposite position in recess 13c of corresponding cross-sectional shape which are formed right through the arms l3, 13 so that the contact bases of said electrodes project to a suitable extent from the face of the arms 13, 13 which is directed towards the stationary electrodes 2, 2' whilst the opposite bases are level with the rear face of the arms. Each of said movable electrodes is securely fixed within its recess by means of a wedge 16 which forms part of a T-shaped member, the transverse flange 16a of which is applied against the rear face of the arms l3, 13 on which it is fixed by means ofa screw 17.

By way of example, practical tests have been carried out in the processing of kerosene or paraffin oil by means of a device of the type hereinabove described. Said device comprised stationary electrodes of graphite 32 mm. in diameter bound with steel sleeves and movable electrodes of graphite having a trapezoidal cross section of 35 50 mm. which were mounted on a rotary cast-iron support. In the case of a voltage of 750 v. and single-phase alternating current at 50 c./s., an effective current intensity of 1,000 amps. and a speed of rotation of the reactor of 3,000 r.p.m., the result achieved was a uniform delivery of 250 Nm lhr. of raw gas having the following composition by volume:

higher acetylene and acetylene compounds 35% higher ethylene and ethylene compounds 15% higher methane and aliphatic compounds 4% hydrogen 46% The mean electric power was 700 kw., with cosy=0.94 and the energy consumption was 2.8 kw./hr. per Nm of gaseous product obtained.

What we claim is:

1. A device for the cracking of organic products in liquid phase by means of a submerged intermittent electric are wherein the electric arc is produced between stationary electrodes and movable electrodes which are secured to a rotary support at uniform angular intervals over a circumference which is concentric with the axis of rotation of said support, characterized iri that the stationary electrodes and the movable electrodes which are in cooperating relation therewith are so arranged that the free extremities of the movable electrodes come successively into contact with the free extremities of the stationary electrodes in a plane at right angles to the axis of rotation of the movable electrode support, means being provided for adjusting the position of the stationary electrodes with respect to the movable electrodes.

2. A device as defined in claim 1, characterized in that the movable electrodes are designed in the form of prisms having a trapezoidal cross-sectional shape, one of the bases of which constitutes theflat contact face of the electrode, said electrodes being advantageously locked in position by keying after insertion in the rota support.

3. A device as de med in claim 1, characterized in that it comprises one or a number of pairs of movable electrodes which are adapted to cooperate with two stationary electrodes.

4. A device as defined in claim 3, characterized in that the rotary support which carries the movable electrodes is constituted by radial arms which are distributed in a number corresponding to the number of movable electrodes about a common hub, the front portions of the movable electrodes considered in the direction of rotation being inserted in the face of said radial arms which is located opposite to the stationary electrodes whilst the projecting rear portions of said movable electrodes are left free.

5. A device as defined in claim 1 characterized in that the rotary support which carries the movable electrodes is constituted by radial arms which are distributed in a number corresponding to the number of movable electrodes about a common hub, the front portions of the movable electrodes considered in the direction of rotation being inserted in the face of said radial arms which is located opposite to the stationary electrodes whilst the projecting rear portions of said movable electrodes are left free.

6. A device as defined in claim 5, characterized in that the movable electrodes are designed in the form of prisms having a trapezoidal cross-sectional shape, one of the bases of which constitutes the flat contact face of the electrode, said electrodes being advantageously locked in position by keying after insertion in the rotary support.

7. A device as defined in claim 5, characterized in that the arms which carry the movable electrodes are designed in the form of fins each having a portion of surface which is inclined in the direction of rotation.

8. A device as defined in claim 7, characterized in that the movable electrodes are designed in the form of prisms having a trapezoidal cross-sectional shape, one of the bases of which constitutes the flat contact face of the electrode, said electrodes being advantageously locked in position by keying after insertion in the rotary support. 

2. A device as defined in claim 1, characterized in that the movable electrodes are designed in the form of prisms having a trapezoidal cross-sectional shape, one of the bases of which constitutes the flat contact face of the electrode, said electrodes being advantageously locked in position by keying after insertion in the rotary support.
 3. A device as defined in claim 1, characterized in that it comprises one or a number of pairs of movable electrodes which are adapted to cooperate with two stationary electrodes.
 4. A device as defined in claim 3, characterized in that the rotary support which carries the movable electrodes is constituted by radial arms which are distributed in a number corresponding to the number of movable electrodes about a common hub, the front portions of the movable electrodes considered in the direction of rotation being inserted in the face of said radial arms which is located opposite to the stationary electrodes whilst the projecting rear portions of said movable electrodes are left free.
 5. A device as defined in claim 1 characterized in that the rotary support which carries the movable electrodes is constituted by radial arms which are distributed in a number corresponding to the number of movable electrodes about a common hub, the front portions of the movable electrodes considered in the direction of rotation being inserted in the face of said radial arms which is located opposite to the stationary electrodes whilst the projecting rear portions of said movable Electrodes are left free.
 6. A device as defined in claim 5, characterized in that the movable electrodes are designed in the form of prisms having a trapezoidal cross-sectional shape, one of the bases of which constitutes the flat contact face of the electrode, said electrodes being advantageously locked in position by keying after insertion in the rotary support.
 7. A device as defined in claim 5, characterized in that the arms which carry the movable electrodes are designed in the form of fins each having a portion of surface which is inclined in the direction of rotation.
 8. A device as defined in claim 7, characterized in that the movable electrodes are designed in the form of prisms having a trapezoidal cross-sectional shape, one of the bases of which constitutes the flat contact face of the electrode, said electrodes being advantageously locked in position by keying after insertion in the rotary support. 